Cranial immobilization system

ABSTRACT

A head immobilization system for immobilizing a patient&#39;s head in a supine position of the patient includes a support rail structure adapted to be coupled to a patient rest. The system can further include a mask frame adapted to be coupled to at least one deformable upper mask sheet. The mask frame is releasably connected to the support rail structure via a first interface section and a second interface section, with at least two pins protruding from the first interface section in a first direction, and at least two pin-receptions provided at the second interface section. Each one of the pin-receptions receives one of the pins. A catch-mechanism for each pin-reception and each corresponding pin allows the pin to be pushed further into the pin-reception in the first direction, but interlocks in case of an attempted withdrawal of the pin from the pin-reception in a second, opposite direction.

RELATED APPLICATION DATA

This application is a continuation of U.S. application Ser. No.17/665,666 filed Feb. 7, 2022, which is a continuation of U.S.application Ser. No. 15/759,690 filed Oct. 25, 2018, which is a nationalphase application of International Application No. PCT/EP2017/059420filed Apr. 20, 2017, the entireties of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an immobilization system forimmobilizing the head of a patient by covering the head's surface atleast partially with an immobilization mask. The present invention maybe used for non-invasive patient immobilization and reproduciblepositioning during stereotactic radiosurgery and radiotherapytreatments.

SUMMARY

Immobilization masks are used for orthopedic applications as well as fortherapeutic or diagnostic procedures, radiotherapy or diagnosticimaging, for which the head of a patient has to be immobilized relativeto a fixed structure and to ensure a high reproducibility of the head'sspatial position during the treatment or diagnostic procedure.

To immobilize a patient's head for radiation therapy or diagnosticimaging, the head is connected to a fixed supporting structure such as apatient bed in a spatially fixed arrangement, and therefore in areproducible position relative to a radiation or imaging device. Forthis purpose, immobilization devices are known, for example from DE 4432 891 A1 or US 2016/0206395 A1, which provide a rigid connectionbetween the head and the supporting structure, wherein the head is heldwithin a mask that has at least one sheet-like layer of a lowtemperature thermoplastic material, which previously has beenindividually adapted to the head in a heated condition so that, afterthe mask has cooled down and cured, the mask tightly fits to the head tobe immobilized.

A problem of known systems is the amount of steps that are necessary toattach the mask to the patient and to adjust it to the patient'sanatomy. This is time consuming and increases the possibility ofhandling errors.

A further problem is the characteristic of many materials that absorb atleast part of the radiation emitted during radiation therapy ordiagnostic imaging.

The present invention provides an immobilization mask system that isfast and easy to handle and that absorbs less radiation than knownsystems.

The system is defined by the appended independent claim. Advantages,advantageous features, advantageous embodiments and advantageous aspectsof the present invention are disclosed in the following and contained inthe subject-matter of the dependent claims. Different advantageousfeatures can be combined in accordance with the invention wherevertechnically expedient and feasible. Specifically, a feature of oneembodiment which has the same or a similar function to another featureof another embodiment can be exchanged with said other feature, and afeature of one embodiment which adds an additional function to anotherembodiment can in particular be added to said other embodiment.

The immobilization system according to the present invention comprises:

-   -   a support rail structure adapted to be coupled to a patient rest        and extending at least on both lateral sides of the patient's        head,    -   a mask frame adapted to be coupled to at least one deformable        upper mask sheet, wherein the mask frame is releasably connected        to the support rail structure via a first interface section and        a second interface section, with at least two pins protruding        from the first interface section in a first direction, and at        least two pin-receptions provided at the second interface        section, wherein each one of the pin-receptions receives one of        the pins, and    -   a catch-mechanism for each pin-reception and each corresponding        pin, which allows the pin to be pushed further into the        pin-reception in the first direction, but which interlocks in        case of an attempted withdrawal of the pin from the        pin-reception in a second, opposite direction.

A first basic component of the inventive system is formed by the supportrail structure which can be releasably or permanently coupled to apatient rest, herein also referred to as “overlay board”. The overlayboard may be adapted to be used on CT-treatment tables and has thereforea flat design. It may comprise a flat carbon sandwich structure whichsupports the patient's body and shoulders, from which the support railstructure which may be also made from carbon protrudes and supports thepatient's neck and head, and which may even extend the treatment table.In order to minimize the risk of collisions, the support rail structuremay be located as close as possible to the patient's head. The supportrail and the patient rest form a support for the patient's body, headand neck and hold them at a fixed position with respect to a CT-table ora treatment table as used during radiotherapy or radiosurgery. Thesupport rail and the overlay board may be made from a radiolucentmaterial, and further may be sized such that the rail and the board fittightly around the patient which will reduce the risk of collisions withthe gantry of an imaging or treatment apparatus.

The mask frame is coupled to a thermoplastic mask that can be deformedso that it adapts to the anterior contour of a patient's head, forexample including the forehead, nose, mouth and chin region. This maskmay comprise more than one thermoplastic layer, wherein the layers maybe molded to the head contour simultaneously or separately, wherein anoptional moldable nose bridge may be provided, as well. In a specificexample, the anterior thermoplastic mask contains two sheets of athermoplastic material. The one or more plane mask sheets are molded tothe head contour by heating them up until they reach a temperature atwhich they become flexible so that they can be molded to a desiredcontour. Each mask sheet consists of a thermoplastic sheet which may beframed on at least two sides by one or more rails of the mask frame.

Moreover, the inventive system comprises means which allow a quickfixation of the mask frame to the support rail structure. According tothe invention these means comprise at least two pins which protrude fromeither the mask frame or the support rail structure, and at least twocorresponding receptacles for these pins on the support rail structureor the mask frame, respectively. A catch-mechanism provided for each oneof the pin-receptacle-pairings only allows the mask frame to be pushedtowards the support rail structure, with the pins further entering thecorresponding receptacles, but prevents an opposite movement of the maskframe away from the support rail structure, with the pins moving in theopposite direction within the receptions.

According to one embodiment of the present invention, thecatch-mechanism comprises saw-toothing on the pin outside surface, whichinterlocks with corresponding saw-toothing on the inside surface of thepin-reception that is held resiliently with respect to thepin-reception, particularly wherein the saw-toothing of thepin-reception is spring loaded with respect to the pin reception.

In other words, the interlocking saw-toothings on the pin and in thepin-reception act as a one-directional ratchet, allowing the pins tomove within the receptions in one direction only, thereby providing anautomatic locking functionality.

According to another preferred embodiment, the catch-mechanism isoperably connected to a release-mechanism for unlocking said interlock,particularly wherein a plurality of catch-mechanisms are operablyconnected to the same release-mechanism. Only by operating therelease-mechanism, the interlock can be released or, more specifically,the two interlocking saw-toothings may be separated from each other,such that the mask frame can be removed from the support rail structureagain. In a more specific example, the release-mechanism may compriseone or more levers, one section of which can be grasped by a person,whereas an opposed section causes a catch to release or “open”. In aneven more specific embodiment, the at least one lever may be rotatablyconnected to the mask frame via one or more film-joints, wherein one endof the lever is provided with the saw-toothing that interlocks with thesaw-toothing of a pin. By moving the second end of the lever in acertain direction, the lever will rotate around the film-joint(s), suchthat the second end of the lever together with its saw-toothing willmove away from the pin and its saw-toothing, thereby releasing theinterlock.

According to another embodiment of the present invention, at least oneof the pins, particularly the pins disposed at each one of the lateralsides of the patient's head in a most caudal position have a guidanceprotrusion that engages into a corresponding notch formed in thepin-reception. Additionally or alternatively, the dimensions of thepin-receptions in the cranial-caudal direction are sized (i.e. “wider”)to allow the pins to enter the pin-receptions even with the mask framebeing tilted up to a predetermined angle with respect to the supportrail structure and around a medial-lateral direction.

This provides a certain degree of freedom when the mask frame togetherwith the mask is pushed onto the support rail structure, thereby causingthe mask to firstly adapt to the contour of the patient's chin. This isbecause it is often not desired to “push” mask layers onto the patient'sforehead in a single anterior-posterior motion, but rather to “tilt” themask when it is pushed onto the patient's face, starting with thechin-portion of the mask being pushed onto the patient's chin.

As already described further above, the inventive system is preferablydesigned to avoid collisions with a gantry surrounding the patient andthe patient table during treatment. Therefore, the support railstructure may extend, particularly within a frontal plane of the patientin the supine position, cranially around a close proximity to thepatient's head.

Further, the first interface section, provided at the support railstructure or the mask frame, or the second interface section, providedat the mask frame or the support rail structure, respectively, maycomprise at least one adjustable stop-mechanism, particularly oneadjustable stop-mechanism on each one of the lateral sides of thepatient's head, that limits the distance by which the pins can be pushedinto the pin-receptions in the first direction by which the mask framecan be pushed towards the support rail structure.

In other words, at least one of the interface sections may comprise aphysical limiter on which the respective other interface comes to restin a final position of the mask frame with respect to the support railstructure. Thus, the mask frame and the mask are prevented from beingpushed further towards the support rail structure and the patient'sforehead beyond a predefined limit.

According to a specific embodiment of the inventive system the at leastone stop-mechanism comprises at least one section having steppedlocating surfaces, and wherein the section is displaceable with respectto the pins, particularly along the support rail structure in acranial-caudal direction.

With a plurality of locating surfaces being provided at differentheights on the interface, and being movable with respect to theinterface, it becomes apparent that the distance at which the interfaceswill come to rest with respect to each other can be adjusted by movingthe section together with the locating surfaces formed thereon. As soonas a “higher” locating surface is replaced by a “lower” locating surfaceat a position at which a corresponding member of the other interfacewill come to rest, the interfaces are allowed to approach each otherfurther. The other way round, replacing a “lower” locating surface by a“higher” locating surface at that position will cause the interfaces tocome to rest with respect to each other at a more distant position.

For adjusting the stop-mechanism, particularly for moving or displacingthe at least one section having the locating surfaces, the stopmechanism may comprise at least one adjustment member, particularlywheel, via which a person may adjust the stop-mechanism. In particular,the adjustment wheel may be connected to the at least one section havinga plurality of locating surfaces via a rack and pinion drive.

While it is conceivable that the displaceable section having thelocating surfaces is adapted to be shifted in a translatory motion withrespect to one of the interfaces on the support rail structure or themask frame, a rotatory motion or even a combined rotatory-translatorymotion is conceivable just as well.

According to a further embodiment of the present invention, the maskframe comprises a first sub-frame adapted to be coupled to at least onefirst deformable upper mask sheet, and a second sub-frame adapted to becoupled to at least one second deformable upper mask sheet, wherein thefirst sub-frame is adapted to be connected to the second sub-frame in adetachable or a non-detachable manner, particularly via one or moredetachable or non-detachable snap-in connections.

Such divided mask frame is in particular useful if more than onedeformable mask-layer is used and it is desired to mold the layers ontothe head contour separately. In such case, a first sub-frame can, in afirst step, be attached to the support rail structure, wherein the oneor more layers connected to the first sub-frame adapt(s) to thepatient's head contour. After the first sub-frame has been put in place,the second sub-frame with one or more mask layers attached thereto canbe installed in the same manner, except that it is connected to thesupport rail structure indirectly via the first sub-frame. In mostcases, there is no need to separate the two sub-frames again after themasks have been molded, such that the two sub-frames may be connected toeach other in a non-detachable manner. However, it is also conceivablethat the two sub-frames may be adapted to be disconnected from eachother again after the respective mask layers have been molded.

So far, mask layers have been described which are molded to the anteriorhead contour of the patient. The inventive system may however furthercomprise one or more similar mask layers provided for the posteriorregion of the head, which are adapted to be molded in a similar manner.Such “rear” masks may comprise a mask frame, as well, by which they canbe held in place with respect to the support rail structure.

Additionally or alternatively to one or more deformable mask sheets forthe posterior region of the patient's head, a posterior head support maybe provided which can be connected to the support rail structure toprovide support for the patient's head when it is immobilized by theinventive system. Such head support may comprise a formed sheet that isshaped to ergonomically accommodate the patient's rear head. Thus, thehead support may also be used as a mold for molding one or more rearmask layers. For example, the head support that has a depression toaccommodate the patient's head is connected to the support railstructure, and one or more heated and therefore deformable rear masklayers are arranged above that depression and are also connected to therail support structure. After that, the patient's head is lowered ontothe head support, wherein the rear mask layers are forced into a shapethat is defined by the depression within the head support and theposterior region of the patient's head. After the thermoplastic materialhas cured again, the new shape of the rear masks is permanent such thatthe rear masks can serve as a head-support for later procedures.

For attaching the head support and/or a frame for one more rear masks,the support rail structure may comprise a rear mask rest which providessupport for the rear mask frame and/or the head support. Further, it isconceivable that the rear mask rest allows a rear mask frame and/or ahead support to be snap-fitted to the support rail structure which willavoid that the head support or the rear mask frame is detached from thesupport rail structure unintentionally. The rear mask rest may be formedby a plurality of protrusions that may extend from the lateral sectionsof the support rail structure in a media-lateral direction.

BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention is described with reference to theenclosed figures which represent preferred embodiments of the invention.The scope of the invention is however not limited to the specificfeatures disclosed in the figures, which show:

FIG. 1 a perspective view of the inventive head immobilization system;

FIG. 2 a lateral view of the system shown in FIG. 1 ;

FIG. 3 a mask frame divided into sub-frames;

FIG. 4 the immobilization system of FIG. 1 with a head support and aposterior mask sheet installed.

DETAILED DESCRIPTION

The embodiment shown in FIG. 1 comprises four pins 7, two on eachlateral side of the support rail structure 1 which is formed by asingle, three-dimensionally formed and unsupported rail that is coupledto the patient rest 2 exclusively on both of its ends. The pins 7 serveas a guidance when the mask frame 3 is moved towards and connected tothe support rail structure 1. Each one of the pins 7 has a saw-toothing10 with a defined distance between the teeth. The teeth feature ahorizontal upper side, wherein the lower side is beveled.

In the shown embodiment, the mask frame 3 (the mask 4 attached theretois not shown) comprises two lateral rails, each one of the rails havingtwo pin-receptions 8 which fit around the corresponding pins 7. Each oneof the rails comprises a release mechanism 12 having a double-lever thatis connected to the rail via two film-joints. It becomes apparent fromFIG. 1 that pushing the “ring-shaped” grasping sections in the middle ofeach rail together will cause the double-lever to bend, with each end ofthe lever being rotated around the corresponding film-joint.Consequently, both ends of the double-lever that extend beyond thefilm-joints are deflected in an opposite direction. Each one of thelever-ends features a saw-toothing 11 within a pin-reception 8, thatinterlocks the saw-toothing 10 on the pins 7.

FIG. 1 shows an unactuated state of the release mechanism 12, with thespring loaded double-lever remaining in a neutral position which willallow the rails of the mask frame 3 to be pushed down over the pins 7since each end of the double-levers will be deflected in a ratchet-likemanner as the saw-toothings 10, 11 slide against each other. Moving themask frame 3 upwards again, away from the support rail structure 1 is,however, prevented by the interlocking saw-toothings 10, 11 that areheld against each other by the elastic double-lever.

To offer more flexibility when installing the mask frame 3 onto thesupport rail structure 1, especially during the mask molding process,the interfaces 5, 6 of the support rail structure 1 and the mask frame 3are designed in a way that the receptacles 8 can be put over the pins 7from an angular position (shown in FIG. 2 ). This makes it easy to moldthe mask around the patient's chin first, and simultaneously insertingthe caudal pins 7 (shown on the left in FIGS. 1 and 2 ) into thecorresponding pin-receptions 8. For doing so, these pins 7 featureguidance protrusions 13 that enter into corresponding notches 14 of thecaudal pin-receptions 8. The notches 14 prevent the mask frame 3 frommoving in a cranial-caudal direction and provide guidance during thedownward movement of the mask frame 3.

Subsequently, the mask frame 3 can be rotated such that the cranial pins7 enter the corresponding pin-receptions 8, as well, and the mask frame3 can be pushed down onto the support rail structure 1 in a translatorymovement with the rails extending parallel to the support rail structure1.

For removing the mask frame 3 from the support rail structure 1 again,the release-mechanism 12 is activated by pressing together thering-shaped grasping sections in the middle of each rail, which willcause the saw-toothings 11 to move away from the correspondingsaw-toothings 10. The mask frame 3 can now be moved upwards and releasedfrom the support rail structure 1.

The embodiment shown in FIGS. 1 and 2 further has an adjustablestop-mechanism 15. When the mask frame 3 is put over the pins 7, thesaw-toothings 10, 11 interlock with each other automatically at the“highest” position. The saw-toothings 10, 11 together with thespring-loaded release-mechanism 12 allow to move the mask frame 3further downwards by continuously pressing it down onto the support railstructure 1. This provides a self-adjustment of the upper mask sheet 4(shown in FIG. 4 ) to the patient's anatomy in subsequent steps. Thestep distance is defined by the size of the teeth of the saw-toothings10, 11, which is 1 mm for the embodiment shown in FIGS. 1 and 2 .

In order to increase the distance between the upper mask 4 and the rearmask/head support 23 (shown in FIG. 4 ), the grasping sections of therelease-mechanism 12 are pressed together and the mask frame 3 is movedupwards until the desired position is reached. As soon as the graspingsections are released, the saw-toothings 10 and 11 interlock again.

In the following, the adjustable stop-mechanism 15 is described, bywhich the minimum distance between the upper mask 4 and the rearmask/head support 23 can be adjustably defined.

The stop-mechanism 15 comprises three sections 16, each section 16having four stepped locating surfaces 17. The sections 16 of each railare connected to a common member that can slide along the lateralsections of the support rail structure 1, and with respect to the pins 7in a cranial-caudal direction. An adjustment wheel 18 that is rotatablyheld with respect to the support rail structure 1 and that is connectedto the common member via a rack and pinion drive 19 allows to adjust thepositon of the sections 16 with respect to the pins 7 and therefore alsowith respect to the mask frame 3 that slides over the pins 7.

As can be seen in FIGS. 1 and 2 , the minimum possible distance by whichthe mask frame 3 can be pushed down onto the support rail structure 1decreases with the sections 16 being moved in a caudal direction, sincelocating surfaces of the mask frame 3 (defined by three pins provided onthe bottom side of the mask frame 3) will come into contact with thecorresponding locating surfaces 17 only in a predetermined position withrespect to the pins 7.

The stop-mechanism 15 allows to pre-adjust the amount by which the uppermask sheet 4 can be pressed onto the patient's face not only during themolding process, but also at a later stage when the patient's head hasto immobilized in a predefined position.

As already indicated above, the mask frame 3 can be adapted to allowmolding of one or more mask sheets. For example, if the upper maskconsists of only one mask sheet 4, the mask frame 3 can be attached tothe support rail structure 1 in a single step. If however, the uppermask consists of two or more mask sheets 4 a, 4 b, the mask sheet 4 aclosest to the patient's skin is molded first, while a first sub-frame 3a is connected to the support rail structure 1 in the manner describedabove. A further mask sheet 4 b which is molded afterwards and therebywill come to rest above the first mask sheet 4 a is coupled to a secondsub-frame 3 b that in turn is coupleable to the first sub-frame 3 a by aplurality of snap-in fasteners 20 as shown in FIG. 3 . Each one of thesnap-in fasteners 20 comprises at least one barb that will prevent thesecond sub-frame 3 b to be released from the first sub-frame 3 a again.Once the two sub-frames 3 a and 3 b are fixedly connected, they can behandled as one unit. They can be attached to or removed from the supportrail structure 1 in a manner that has been already described furtherabove in connection with the single frame 3.

FIG. 4 further shows an undeformable head support 23, which may besupplemented or replaced by deformable mask sheet 22. Both, the headsupport 23 and the rear mask sheet 22 may comprise a frame structure(not shown) which may be snap-fitted to the protrusions 24 (shown inFIG. 1 ) and may therefore be detachably connected to the support railstructure 1.

Any of the mask sheets 4, 4 a, 4 b can be connected to the correspondingmask frame 3, 3 a, 3 b by being inserted and glued into slots of themask frame 3, 3 a, 3 b (shown in FIGS. 1 and 2 ). Alternatively, themask sheets 4, 4 a, 4 b can be laser-welded to the corresponding maskframes 3, 3 a, 3 b.

In the following, possible configurations for the overall mask fixationsystem are described:

Mask configuration 1:

-   -   Head support 23 (may be removed after mask molding)    -   Rear mask 22 (custom made to fit patient)    -   Middle mask 4 a (custom made to fit patient)    -   Top mask 4 b (custom made to fit patient)

Options for 1:

-   -   Middle and top mask sheet 4 a, 4 b may come rigidly prefixed        together by means of lateral rails of mask frames 3 a, 3 b    -   Instead of a middle and a top mask 4 a, 4 b the upper mask        consist of just a top mask 4 (no middle mask 4 a in this        configuration)    -   Additional moldable nose bridge fixation, that is molded to the        patient's nose bridge out of thermoplastic pallet material and        located between the patient and the middle and/or top mask 4 a,        4 b (custom made to fit patient)    -   Optionally eye opening in upper mask    -   Optionally face opening in upper mask    -   Optionally forehead opening in upper mask

Mask configuration 2:

-   -   Head support 23 (cannot be removed after mask molding)    -   Upper mask (custom made to fit patient), attached to mask frame

Options for 2:

-   -   Additional middle mask 4 a    -   Additional moldable nose bridge fixation, that is molded to the        patient's nose bridge out of thermoplastic pallet material and        located between the patient and the middle and/or top mask 4 a,        4 b (custom made to fit patient)    -   Optionally eye opening in upper mask    -   Optionally face opening in upper mask    -   Optionally forehead opening in upper mask

The patient rest 2 (shown in FIGS. 1, 2 and 4 ) is typically secured toa treatment table by means of mounting brackets (not shown) which mayposition the patient rest 2 to the treatment table's indexing system inan interlocking manner for a defined and reproducible position. Thepatient rest 2 may be attached to the treatment table in a force-lockingmanner, as well as by brackets that embrace the table top and can belocked by a fastener. The patient rest 2 has a material minimized designthat reduces it's effects on attenuation and dose build-up when theradiation beam has to pass the patient rest 2. The patient rests 2support rail structure 1 incorporate the mask fixation and connectionpoints for the upper and lower mask shell, the rear head support 23 andthe height adjustment unit 15. To minimize the collision risk with alinear accelerator, the support rail structure 1 of the patient rest 2is located as close as possible to the longitudinal middle axis of thepatient's head. The cranial bar extending in a medial-lateral directionand connecting the lateral sections of the support rail structure 1 islocated as close as possible to the head, following the head's anatomy.

In the following, preferred workflows in the context of the inventivehead immobilization system are described:

Workflow Mask Molding

-   -   Place the patent rest 2 onto the CT-tabletop or treatment        tabletop and fasten it    -   Attach the head support 23 to the support rail structure 1 by        hanging it onto the lateral protrusions 24    -   Heat the thermoplastic material of the masks to the molding        temperature    -   (Optional) attach the posterior mask together with frame 22 to        the support rail structure 1 by clipping it into the lateral        protrusions 24    -   (Optional) mold the posterior mask to the patient's back of the        head    -   Place the patient into the posterior mask, respectively the head        support 23    -   Adjust the two lateral stop-mechanisms 15 to the dedicated        vertical home position    -   Attach mask 4 a together with frame 3 a to the support rail        structure 1 by clipping it to the spring loaded catch-mechanism        9. The mask 4 a will be secured in the dedicated vertical        position automatically.    -   (Optional) mold a nose bridge to the patients nose using the        thermoplastic material    -   (Optional) attach mask 4 b together with frame 3 b to the mask 4        a and frame 3 a by clipping together the sub-frames 3 a and 3 b.        The middle mask 4 a and the upper mask 4 b will be permanently        joint.

Work-Flow Patient Fixation

-   -   Place the patient rest 2 onto the treatment tabletop and fasten        it    -   (Optional) attach the head support 23 to the support rail        structure 1 by hanging it into the lateral protrusions 24    -   (Optional) attach the posterior mask together with frame 22 to        the support rail structure 1 by clipping it into the lateral        protrusions 24    -   Place the patient into the posterior mask    -   Adjust the two lateral stop-mechanisms 15 to the dedicated        vertical home position    -   Attach mask 4 a together with frame 3 a and mask 4 b together        with frame 3 b (optionally just mask 4 a with frame 3 a) onto        the patients head by clipping it into the spring loaded        catch-mechanism 9. The mask(s) 4 a/4 b will be secured in the        dedicated vertical position automatically.    -   If the mask(s) 4 a/4 b is/are too tight or too loose, adjust the        tightness with the stop-mechanisms 15 to tighten/loosen mask(s)        4 a/4 b by enlarging or reducing the distance between the rear        head mask/head support 23 and the upper mask(s) 4 a/4 b.    -   To loosen the mask(s) 4 a/4 b, actuate the release-mechanism 12        and lift it, until the dedicated vertical position is reached.        Adjust the sections 16 of the stop-mechanisms 15 to the suitable        position.    -   To tighten the mask(s) 4 a/4 b, adjust the sections 16 of the        stop-mechanisms 15 to the suitable lower position. Push the        mask(s) 4 a/4 b down until the dedicated vertical position is        reached.    -   To remove the mask(s) 4 a/4 b after treatment activate the        release-mechanism 12 and lift the mask(s) 4 a/4 b. Remove the        rear head mask and the head support 23 by lifting them up.

1. A mask system for immobilizing a patient's head relative to a supportrail structure of a head immobilization system, comprising: at least onedeformable patient mask sheet; and, a mask frame coupled to at least onedeformable patient mask sheet, the mask frame including: pluralinterface sections, each interface section including a releasable pinreceiver having a sawtooth catch structure on a surface, wherein thereleasable pin receiver is adapted to receive a pin extending from asupport rail structure of a head immobilization system, and wherein thesaw tooth catch structure is adapted to engage a corresponding saw toothstructure on the pin to allow the pin to be pushed progressively furtherinto the releasable pin receiver, but to prevent removal of the pin fromthe pin receiver unless released; and a release mechanism includingoperating sections that, when operated, cause the releasable pinreceiver to release from engagement with the corresponding pin.
 2. Thesystem of claim 1, wherein the system includes plural deformable patientmask sheets.
 3. The system of claim 2, wherein one mask sheet is moldedto the patient's nose bridge.
 4. The system of claim 1, wherein thepatient mask sheet is a thermoplastic sheet.
 5. The system of claim 1,wherein the patient mask sheet includes eye holes.
 6. The system ofclaim 1 including a rear patient mask sheet and a top patient masksheet.
 7. The system of claim 1 including a rear patient mask sheet, amiddle patient mask sheet, and a front patient mask sheet.
 8. The systemof claim 1, wherein the operating sections are tabs that when squeezedtogether cause the saw toothed catch structure to disengage the pins onthe support rail structure.
 9. The system of claim 8, wherein the tabsare ring-shape.
 10. The system of claim 1, wherein the releasable pinreceiver is spring biased into closed position retaining the pin.
 11. Asystem for immobilizing a patient's head relative to a headimmobilization system, comprising: a support rail on the headimmobilization system, the support rail including at least one pinhaving a saw toothed surface; a deformable plastic sheet; and a maskframe, the mask frame including: an engagement system for engaging aportion of the deformable patient mask sheet and plural interfacesections, each interface section including a releasable pin receiverhaving a sawtooth catch structure on a surface, wherein the releasablepin receiver is adapted to receive the pin extending from the supportrail structure and wherein the saw tooth catch structure is adapted toengage a corresponding saw tooth structure on the pin to allow the pinto be pushed progressively further into the releasable pin receiver, butto prevent removal of the pin from the pin receiver unless released; anda release mechanism including operating sections that, when operated,cause the releasable pin receiver to release from engagement with thecorresponding pin.
 12. The system of claim 11, wherein the mask frameincludes two lateral rails, each including the plural interfacesections.
 13. The system of claim 11 including an adjustment mechanismthat varies the distance between the support rail and the lateral rail.14. A radiation therapy system, comprising: a radiation therapy device;a patient support structure configured to be positioned relative to theradiation therapy device, the patient support structure including a pairof support rails, each rail including a pin with a saw tooth structureon at least one face; and a mask system, including: at least onedeformable patient mask sheet; and plural mask frames, each mask frameincluding: an engagement system for engaging a portion of at least onedeformable patient mask sheet and plural interface sections, eachinterface section including a releasable pin receiver having a sawtoothcatch structure on a surface; wherein the catch structure is adapted toreceive the pin extending from the support rail structure and to engagea corresponding saw tooth structure on the pin to allow the pin to bepushed progressively further into the releasable pin receiver, but toprevent removal of the pin from the pin receiver unless released; and arelease mechanism including operating sections that, when operated,cause the releasable pin receiver to release from engagement with thecorresponding pin.
 15. The radiation therapy system of claim 14, whereinthe radiation therapy device is a linear accelerator.